The invention relates to a multiplexing method used in a TDMA radio system, in which method connections are set up by means of signals that are transmitted in time slots and that are modulated before the transmission, and wherein a signal consisting of bits is received and channel-coded into channel-coded signals each of which is interleaved into blocks of a predetermined size.
In digital radio systems, information can be transmitted by means of binary symbol sequences. Binary symbol sequences constitute a signal to be transmitted, and the placement of binary symbol sequences in the signal to be transmitted is called digital modulation. Digital modulation is carried out in practice by a digital modulator. In the simplest form, the modulator places the binary symbol sequences in the signal regardless of the blocks that have already been transmitted or that will be transmitted later. The modulator may place the symbols in multiple levels in the signal in order to form several different waveforms. The prior art teaches the use of for example the digital QPSK modulation method as a multilevel modulation method.
In GSM systems, it is possible to use the TDMA multiple access method wherein signals are transmitted in the form of bursts in time slots. A speech signal is coded into time slots by different coding methods. A speech signal is formed into blocks of for example 260 bits that are channel-coded into signals of typically 456 bits. The channel-coded signal is interleaved in order to decrease the effect of possible interfering signals on the information signal. The interleaving can be carried out for example such that the 456 bits are divided into four blocks each of which consists of 114 bits. Each block fills one burst in whole. After the interleaving the signal is modulated, whereafter it is transmitted to the radio path.
The amount of traffic and the number of users continue to increase in radio systems. Since the bandwidth used in radio systems is limited, the number of available channels in a radio system is at times insufficient for all the users to be able to set up a connection. If a connection from a base station to a subscriber terminal, for example, can be set up, the connection may be relatively slow in some cases and therefore transmission of information takes a long time. The interleaving methods used in the prior art have not always been sufficiently effective so that the capacity and data rate in the radio system could be increased in an easy manner.
The purpose of the invention is to implement a multiplexing method and a transceiver realizing the method, such that the aforementioned problems can be solved. This is achieved with a multiplexing method of the type described in the introduction, characterized by multiplexing at least two blocks together, followed by modulating said blocks into the same time slot with a modulation method that is adapted to the number of the blocks to be modulated, and transmitting the modulated blocks as a communication signal in a time slot, so that the transmission speed of the communication signal and the number of the connections to be established can be increased.
The invention also relates to a transceiver that is used in a TDMA radio system and that sets up a connection to another transceiver by transmitting modulated signals in time slots, and that receives a signal consisting of bits, and that comprises coding means for channel-coding the received signal into channel-coded signals, and interleaving means for interleaving each channel-coded signal into blocks of a predetermined size.
The transceiver according to the invention is characterized in that the transceiver comprises multiplexing means that receive blocks from the interleaving means and that multiplex at least two blocks together, and modulation means that modulate said blocks based on the number of the blocks to be multiplexed, whereafter the modulated blocks are transmitted as a communication signal in a time slot, so that the transmission speed of the communication signal and the number of the connections to be established can be increased.
The preferred embodiments of the invention are disclosed in the dependent claims.
The basic idea of the invention is that the transceiver multiplexes the interleaved signal blocks, so that when the blocks are modulated by a multilevel modulation method, several signal blocks can be transmitted in the same burst. The transceiver also demodulates the signal it has received from the radio path by a multilevel modulation method and performs demultiplexing so that the signal blocks that were in the same burst can be interleaved again.
The multiplexing method and the transceiver according to the invention provide several advantages. The method makes it possible to increase the data rate of a signal used over a connection between two transceivers. The method also enables an increase in the number of subscriber terminals, for example. The structure of the transceiver does not have to be modified greatly, but the presently used structural parts can be utilized mostly without any changes.